Production of photographic material



Nov. 10, 1959 R. B. COLLlNS ETAL PRODUCTION OF PHOTOGRAPHIC MATERIALFiled Nov. 10, 1958 United-States I Patent ice PRODUCTION orPHOTOGRAPHIC MATERIAL Ronald Bernard Collins and Stanley FrederickWilliam Welford, Ilford, England, assignors to Ilford Limited, Ilford,England, a British company Application November-10, 1958, Serial No.772,956

Claims priority, application Great Britain November 18, 1957 2 Claims.(Cl. 117- 34 This invention relates to the production of colourphotographic materials. I

In one main method of colour photography there is provided aphotographic element which comprises a support carrying three silverhalide photographic emulsion layers which are differentially sensitiveto three regions of the visible spectrum, normally blue, green and red,and which contain compounds, so-called colour couplers, which willcombine with the oxidation products of aromatic primary amino developingagents used to develop silver images in the layers to form dye imageswhich are complementary to the utilised sensitivity of the respectivelayers.

Thus, for example, the photographic element may comprise the followinglayers in super position:

(a) Colourless film support.

(b) Silver halide emulsion layer sensitised to red light by means of anappropriate sensitising dye and containing a colour coupler yielding acyan image.

(c) Silver halide emulsion layer sensitised to green light by means ofan appropriate sensitising dye and containing a colour coupler yieldinga magenta image.

(d) A yellow filter layer the colour of which may be readily destroyed.

(e) Silver halide emulsion layer having its natural sensitivity to bluelight and containing a colour coupler yielding a yellow image.

The assembly may contain other layers, e.g. outer layers, maskinglayers, substratum and supercoat layers, according to the specificrequirements in the product. The specified yellow filter layer (d) actsas a barrier to blue light reaching layers (b) and (c). I,

When such a layer is processed by exposure, development in an ordinaryblack and white developer, reexposed, re-developed in a developer whichis an aromatic primary amine such as N.N- diethyl-p-phenylene diamine,or its closely analogous compounds, and the silver removed from theproduct, there is obtained a film product which has positive images incyan, magenta and yellow in layers (b), (c) and'(e)' respectively, andwhich thus presents by transmitted light a more or'less true colourrecord of the subject to which the film was exposed.

Such colour photographic material is of relatively slow speed, andthough several factors contribute to this, one

important factor is that there is a tendency for the colour 7 couplerswhich are added to the emulsion layers to reduce very considerably thephotographic speed of the layers. This is particularly so in the case ofthe redsensitised layer where the colour couplers yielding cyan dyeswhich are commonly used are phenolic compounds or naphtholic compounds.It appears probable that the colour coupler tends to displace thered-sensitising dye from the silver halide grains and thus, by reducingthe effect of the dye, reduces the speed of the emulsion to red lightvery considerably. Attempts have been made to overcome this difficultyby a careful selection of red-sensitising dye (compare, for example,British Patent No.

' 2 625,992), but there are limits to this possibility and in fact nored-sesitising dye of adequate sensitising effect has yet been foundwhich will be wholly unaffected by the addition to the emulsion of aphenolic type colour coupler.

It has now been found, however, that the reduction in speed of theemulsion consequent on the addition of the colour coupler takes placeprimarily While the emulsion is in liquid bulk form and will occur verymuch more slowly, if at all, after the emulsion has been coated andset-as, a layer onthe support. Thus the emulsion, containing the colourcoupler, deteriorates in speed with time so that, as it is coated, thespeed of the coating obtained decreases with consequent change in colourbalance.

According to the present invention, therefore, in the method ofproducing colour photographic materials whichcom'prises applying to asupport layer a silver halide photographic emulsion which contains acoloursensitising dye and .a colour coupler, or other compound thepresence of which tends to reduce the sensitivity of the emulsion, theemulsion containing the colour-sensitising dye and a solution of thecolour coupler or said other compound are intimatelyadmixed in therequired proportion at or near the siteof the coating device and themixture is coated with the minimum possible time delay between the timeof mixing and the time when the emulsion is coated, and the coatedemulsion is set and dried with the minimum of delay.

Various mechanical mixing devices known per se may be employed toproduce the final emulsion for coating. Thus theemulsion and additivesolution may be pumped as separate streams to a mixing cylinder andpass, via baflies, directly to the coating head of the coating machine.

Any of the well known methods of coating photographic emulsions may beemployed, but generally one difference in working must be employed. Insome methods part of the emulsion passing the coating head runs back tothe coating head, i.e. the excess over the requirement (set by thethickness of the layer to be coated) is returned to the main bulk ofemulsion. These methods cannot generally be employed in accordance withthe presrent invention since it means that part of the emulsion leavingthe coating head, and which is still deteriorating in speed owing to theeffect of the additive, becomes mixed in with the fresh emulsion thusreducing its overall speed. Accordingly, such methods must generally beadopted with the variation that any run-back of'emulsion is diverted anddiscarded. However, if the percentage run-back is not too excessive andthe coating speed is fairly high, it is possible to set up equilibriumconditions in which, although there is some run-back, the photographicspeed of the emulsion actually coated onthe support is not undulyreduced.

Preferably those methods of coating will be employed in which there isno run-back of emulsion to the coating head, i.e. methods in which thequantity of emulsion passed by the coating head is strictly metered tothat required to give the desired coating thickness. Moreover, it isimportant that at all times the quantity of prepared emulsion waiting tobe coated shouldbe the min imum possible. For this reason so-calledslab-coating is preferred. The method normally provides a small surplusof emulsion which is recirculated and it may therefore be provided thatany increase in the overflow rate is electronically detected and theinformation fed back to control the coating speed. In this way it isarranged that any increase in overflow automatically increases coatingspeed and therefore the rate of pick-up of the emulsion, so that theoverflow is immediately compensated.

Alternatively, various methods whereby the prepared Patented Nov. 10,1959 emulsion is extruded on to the support may be employed.

It has been found that, by employing the method of this invention forthe coating of the red-sensitive layer in the production of a colourfilm which, as normally prepared, has a Weston speed of about 10, it ispossible to obtain film of identical colour characteristics but a Westonspeed of 60 to 80.

The following example will serve to illustrate the invention:

Example A silver halide emulsion containing 188 gms. of silver and 350gms. of gelatin is spectrally sensitised to the red end of the spectrumduring its manufacture by the addition of 600 mls. of a 1:2000 solutionof 3:3'-dimethyl 6:6 dimethoxy 9[1:5 dimethyl 2 phenyl- 3-oxopyrazolinyl (4)] thiacarbocyanine bromide: 260 gms. of gelatin and 100mls. of wetting agent are added and after adjustment of the pH to 7.4the total bulk is made up to 11,000 gms. The colour former solution,which is the additive described in this example, contains 310 gms. ofgelatin and 170 gms. of colour former (to form a cyan image) added as a5% solution of the sodium salt ofl-hydroxy-2-naphthoyl-stearylaminel--sulphonic acid. After adjustment ofits pH to 7.4 the solution is diluted to a total bulk of 11,000 gms. Thetwo solutions thus compounded have approximately equal viscositiesmeasured as cps. at the temperature of coating, 355 C.: this equality ofviscosity assists mixing: owing to the interaction of the colour formerwith the gelatin of the emulsion the viscosity of the mixed solutionsrises to 18 cps.

The emulsion and colour former solutions are held in vesselsthermostatically controlled at the coating temperature and each is fedinto similar metering pumps driven at the same speed from a motor drivenvariable speed gear box so that although the ratio of the mixing of thetwo fluids is invariable yet the total flow can be adjusted to meet therequirements of coating. The metering pumps are of conventional design.The two metered flows are then fed into the mixing cylinder.

A suitable mixing chamber is illustrated in the accompanying drawing. Itconsists of a small squat form cylinder 1 mounted vertically: a thickrotating spindle 2 runs centrally down the cylinder having its lowerbearing on the base and its upper bearing on a bafiie 11 across thecylinder. Attached to the spindle at its lower end is a small plasticcovered magnet 3 which serves a dual purpose; primarily it is the drive,this being achieved magnetically from outside by means of the rotatingmagnet 4 driven from the gear box 5 and the motor 6. Secondarily itserves as the first stage of mixing as the two liquids are fed into thissection of the cylinder from opposite entry ports 7 and 8. This methodof driving obviates the need for glands thus reducing the chances ofcontamination or the introduction of air bubbles. The upper portion ofthe cylinder 1 is divided by baflies 9 into segments, the liquid flowbetween the segments being at the periphery of the battles Mounted onthe spindle and running closely between the baffles 9 are discs 10, themixing being brought about by the rotation of the discs 10, the upwardflow of liquid taking place at the outer edges of the bafiles 9 where itis sheared by the rotating discs 10. These may operate at 100 rpm. Themixed liquid then flows through holes in the baffie supporting the upperbearing, through the exit port 12 at the top of the cylinder 1, and thendirect to the coating head where it is continuously coated on film baseat a coating speed of 10 feet per minute. The coated film passes, a fewseconds after being coated, through a chill-box which sets the emulsion,and then through a drying chamber.

On examining a 500 foot length of the coating by sensitometric exposuresthrough a filter passing only the longer wavelengths of the spectrum, nochanges in speed were found, the whole coating being quite uniform.

In other experiments not employing the method described above butworking with the same final emulsion, a gradual loss of red-sensitivitywas found amounting to log E 0.30 over the period of time that would betaken in coating a 500 foot length (50 minutes).

Whilst the invention has been described with particular reference to thecase where the additive is a colour coupler, it will be understood thatit is applicable to any case where the additive is one which tends toreduce the sensitivity of the liquid emulsion over a period of time.Thus it also includes the case where the additive is a dyestuff, e.g. anazo dyestuif, which has such an effect.

What we claim is:

1. In a method of producing colour photographic materials whichcomprises: preparing a color sensitized silver halide emulsion by addinga color sensitizing dye to a silver halide emulsion; thereafter addingto the sensitized emulsion a color coupler the presence of which tendsto reduce the sensitivity of the emulsion, and thereafter applying theresulting composition to a support layer as a coating thereon; theimprovement which comprises: deferring the addition of the color couplersolution to the color sensitized emulsion until the color sensitizedemulsion has been brought to the site at which it is to be applied tothe support layer and thereupon admixing the color coupler with thecolor sensitized emulsion; and promptly thereafter applying the freshlyformed admixture to the support layer whereby the support is coated withthe minimum possible time delay between the time of admixing and thetime of coating, and the coating is set and dried with the minimumdelay.

2. In a method of producing colour photographic materials whichcomprises: preparing a color sensitized silver halide emulsion by addinga color sensitizing dye to a silver halide emulsion; thereaftercontinuously adding to the sensitized emulsion a color coupler thepresence of which tends to reduce the sensitivity of the emulsion, andthereafter continuously applying the resulting composition to a supportlayer as a coating thereon; the improvement which comprises: deferringthe continuous addition of the color coupler solution to the colorsensitized emulsion until the color sensitized emulsion has been broughtto the site at which it is to be applied to the support layer andthereupon continuously admixing the color coupler with the colorsensitized emulsion; and promptly thereafter continuously applying thefreshly formed admixture to the support layer whereby the support iscoated with the minimum possible time delay between the time of admixingand the time of coating, and the coating is set and dried with theminimum delay.

References Cited in the file of this patent UNITED STATES PATENTS2,280,300 Potter et a1. Apr. 21, 1942 2,295,276 Wilmanns et al. Sept. 8,1942 2,415,644 Leonhard et al. Feb. 11, 1947

1. IN A METHOD OF PRODUCING COLOUR PHOTOGRAPHIC MATERIALS WHICHCOMPRISES: PREPARING A COLOR SENSIZED SILVER HALIDE EMULSION; THEREAFTERADDING TO THE TO A SILVER HALIDE EMULSION; THEREAFTER ADDING TO THESENSITIZED EMULSION A COLOR COUPLER THE PRESENCE OF WHICH TENDS TOREDUCE THE SENITIVITY OF THE EMULSION, AND THERETENDS TO REDUCE THESENSITIVELY OF THE EMULSION, AND THERELAYER AS A COATING THEREON; THEIMPROVEMENT WHICH COMPRISES; DEFERRING THE ADDITION OF THE COLOR COUPLERSOLUTION TO THE COLOR SENSITIZED EMULSION UNTIL THE COLOR SENSITIZEDEMULSION HAS BEEN BROUGHT TO THE SITE AT WHICH IT IS TO BE APPLIED TOTHE SUPPORT LAYER AND THEREUPON ADMIXING THE COLOR COUPLER WITH THECOLOR SENSITIZED EMULSION AND PROMPTLY THEREAFTER APPLYING THE FRESHLYFORMED ADMIXTURE TO THE SUPPORT LAYER WHEREBY THE SUPPORT IS COATED WITHTHE MINIMUM POSSIBLE TIME DELAY BETWEEN THE TIME OF ADMIXING AND THETIME OF COATING, AND THE COATING IS SET AND DRIED WITH THE MINIMUMDELAY.